Vertebral body manipulation device and methods

ABSTRACT

Featured is a vertebral body manipulation instrument or vertebral body manipulation device being configured and arranged to allow correction of vertebral translation. Such a vertebral body manipulation device embodies one or more identical modules that are configured as needed for correcting the deformity. Such a vertebral body manipulation device also is usable in combination with a plurality of vertebral anchors, such vertebral anchors being any such vertebral anchors as are known to those skilled in the art (e.g., conventional spinal pedicle screw instrumentation) or hereinafter developed so as to form a spinal implant system. Also featured are treatment methods utilizing such a vertebral body manipulation device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application62/488,347 filed on Apr. 21, 2017, the entire contents of which isincorporated herein by reference in its entirety.

FIELD OF DISCLOSURE

The present disclosure relates to instruments and methods forstabilizing and manipulating the spine. More particularly, the presentdisclosure relates to a vertebral body manipulation instrument for usein connection with surgical treatment modalities for the spine.

BACKGROUND OF THE DISCLOSURE

Spinal deformity (e.g., spondylolithesis) often requires surgicalcorrection. A common way to reduce spinal deformity is to use plier-typeinstruments. This generally requires multiple instruments andmanipulations in different spatial planes to correct the spinaldeformity. Unfortunately, fine control of such plier-type instrumentsmay be difficult to achieve, especially while changing from one spatialplane to another. Additionally, such plier-type instruments aretypically limited to open surgery. Disadvantageously, such instrumentsfrequently use rods that are mounted over pedicle screws to operate,which constrains the maneuverability of the vertebral bodies, making iteven more difficult to correct the spinal deformity. Another impedimentof prior art instrumentation is that profiling or customizing the rodsis often difficult to determine in advance of the surgical procedure.Thus, there is an urgent unmet need for new and improved vertebral bodymanipulation devices and methods to facilitate spinal surgeries thatovercome the problems of prior art instruments described above.

SUMMARY OF THE DISCLOSURE

The present disclosure features a vertebral body manipulation devicethat is used in combination with a plurality of vertebral anchors, whichmay be any of a variety of vertebral anchors known to those skilled inthe art (e.g., spinal pedicle screws and the like), to form a spinalimplant system. Such a vertebral body manipulation instrument or deviceis configured and arranged so as to allow correction of the translationas well as application of distraction across a segment in an independentfashion. In further embodiments, such a vertebral body manipulationdevice or instrument embodies one or more identical modules that areconfigured as needed for correcting the deformity, and in moreparticular embodiments each instrument/device includes a plurality ofsuch modules. Such a vertebral body manipulation device allowsreorientation of the vertebral segment(s) as needed.

In further embodiments, each module includes two separate assemblies: abase unit that is configured and arranged so as to attach to a pluralityof vertebral anchors and a vertebral body manipulation device thatcontrols the movement of the module.

The vertebral body manipulation device is unique in that it may be usedin combination with almost any currently available vertebral anchor. Itmay also be used with both “open” surgical procedures and percutaneouspedicle screw techniques. It allows a continuous adjustment and allowsfor manipulation of the vertebral segment to occur with intuitiveuncoupled motion.

In further embodiments, the base unit includes two base elements, eachbase element including at least a threaded pole, a smooth pole, and aquick-lock mechanism at one end of the threaded and smooth poles. Thequick-lock mechanism may be configured and arranged so as to mate with aspinal implant via a screw extension and pedicle screw. In exemplaryembodiments, the quick-lock mechanism may be configured and arranged tomate with the screw extension connected to the spinal implant.

The threaded pole is threaded along its length and in furtherembodiments, such a pole is a tubular member. As described furtherherein, the thread surface of the threaded pole corresponds to the samethread surface as that embodied in the primary device and the primarydevice threads onto the threaded pole base. It is contemplated withinthe scope of the disclosure that the thread surface may lend amechanical advantage that allows for the relative movement of thevertebral bodies.

In further embodiments, the primary device includes two portions thatare connected to one another by two parallel sets of bars that areallowed to pivot in one plane around a central point forming a double‘X’ configuration (e.g., a scissor mechanism). The primary device may beconfigured and arranged so as to separately control movement along theAnterior-Posterior (AP), Superior-Inferior (SI), and Left-Right (LR)directions of the Left-Posterior-Superior (LPS) patient coordinatesystem. Depending how the one or more modules are configured, placed,and oriented on the spine, the three DoF for each module can achieve amulti-degree of freedom correction (e.g., 5 or 6 DoF).

In exemplary, illustrative embodiments, the primary device or reductioninstrument is mounted via a footlink to, for example, a DePuy ExpediumViper V2 extension and Expedium pedicle screw. The Expedium pediclescrew is a polyaxial screw, and during normal function it becomes rigidwhen locked to a rod in a rod screw construct as a result of theconstruct rod being forced by a nut into a bushing which results in theball at the head of the screw being forced against the tulip of thescrew, and thus by friction, constrains the screw. This mechanism can beengaged with the vertebral body manipulation instrument. The vertebralbody manipulation device of the present disclosure works with allexisting pedicle screw systems, from any manufacture, to convert apolyaxial screw to a functionally a screw.

According to further aspects, the present disclosure also featuresmethods for stabilizing a spine using such an implant system and/orvertebral body manipulation device as described herein. Also featuredare methods for treating spondylolithesis using surgical techniques andusing the vertebral body manipulation device and/or implant system ofthe present disclosure. Such methods are usable with both “open”surgical procedures and percutaneous pedicle screw techniques. Suchmethods further include continuous adjustment and manipulation of thevertebral segment to occur with intuitive uncoupled motion.

As the vertebral body manipulation device of the present disclosureembodies a mechanism or quick-lock mechanism for coupling the instrumentto any currently available spinal implant utilizing a plurality ofvertebral anchors as the implant, such a vertebral body manipulationdevice is easily adaptable to use with such an implant. Thus, avertebral body manipulation device of the present disclosure would notrequire redesign of a current implant or vertebral anchor.

In an aspect, a vertebral body manipulation instrument according to thedisclosure may include: at least one module including a first base unit,a second base unit, a threaded pole, a smooth pole, and a scissorsmechanism; the first base unit having an upper end connected to thethreaded pole and a lower end configured to mate with a first vertebralanchor; the second base unit having an upper end connected to the smoothpole and a lower end configured to mate with a second vertebral anchor;and the scissors mechanism connecting the first base unit to the secondbase unit and the threaded pole to the smooth pole.

In an embodiment, the scissors mechanism connects to the first base unitand the second base unit via a revolute joint.

In an embodiment, the scissors mechanism connects to the threaded polevia a revolute joint mounted on a threadable coupling configured tointerface with a threaded portion of the threaded pole.

In an embodiment, the scissors mechanism connects to the smooth pole viaa revolute joint mounted on a slidable coupling configured to interfacewith a smooth portion of the smooth pole.

In an embodiment, the vertebral manipulation instrument is able toconvey three degrees of freedom of movement to the first and secondvertebral anchors when the lower end of the first base unit is matedwith the first vertebral anchor and the lower end of the second baseunit is mated with the second vertebral anchor.

In an embodiment, the first base unit and the second base unit each havea quick-lock mechanism configured to secure the first and secondvertebral anchors. In an embodiment, the threadable coupling includes arotary joint. In an embodiment, the threadable coupling includes a nutand a nut cage configured to interface with a plurality of grooves onthe threaded pole and a plurality of bearing balls positioned betweenthe threaded coupling and the nut cage, the nut including a recessedthread configured to provide clearance relative to the plurality ofgrooves on the threaded pole.

In an aspect, the disclosure provides a method for surgical treatment ofspondylolithesis comprising the step(s) of: providing the vertebralmanipulation instrument of claim 1, wherein each of the at least onemodules is configured and arranged to cause translation or rotation of avertebral segment along an Anterior-Posterior (AP), Superior-Inferior(SI), and/or Left-Right (LR) axis of a Left-Posterior-Superior (LPS)patient coordinate system. In an embodiment, the method further includesthe step(s) of: securing the manipulation instrument to a spine usingspinal pedicle screw instrumentation.

In an aspect, the disclosure provides a surgical manipulationinstrument, that includes at least one module including a first baseunit, a second base unit, a threaded pole, a smooth pole, and a scissorsmechanism; the first base unit having an upper end connected to thethreaded pole and a lower end configured to mate with a first vertebralanchor; the second base unit having an upper end connected to the smoothpole and a lower end configured to mate with a second vertebral anchor;and the scissors mechanism connecting the first base unit to the secondbase unit and the threaded pole to the smooth pole, wherein the scissorsmechanism confers three degrees of freedom of movement to the first andsecond vertebral anchors when the lower end of the first base unit ismated with the first vertebral anchor and the lower end of the secondbase unit is mated with the second vertebral anchor.

In an embodiment, the scissors mechanism connects to the threaded polevia a revolute joint mounted on a threadable coupling configured tointerface with a threaded portion of the threaded pole.

In an embodiment, the threadable coupling is operated with a wrench or atorque wrench.

In an embodiment, the scissor mechanism is configured to reduce changesin mechanical advantage.

In an embodiment, the instrument is configured to maintain a head of thefirst vertebral anchor at the same relative orientation and level of ahead of the second vertebral anchor.

In an embodiment, the instrument is configured to adjust the distancebetween the head of the first vertebral anchor and the head of thesecond vertebral anchor.

In an embodiment, the instrument is configured to manipulate one or morevertebral bodies by applying a rocking and/or twisting motion to thefirst and/or second vertebral anchors which have been anchored in theone or more vertebral bodies.

In an aspect, the disclosure provides a fastener that includes: a nuthaving a threaded inner surface and an outer surface including at leastone circumferential nut guide; and a sleeve configured to rotatablyinterface with the at least one circumferential nut guide.

In an embodiment, the sleeve has an inner surface including at least onecircumferential sleeve guide configured to align with the at least onecircumferential nut guide.

In an embodiment, the at least one circumferential nut guide houses aplurality of ball bearings when aligned with the at least onecircumferential nut guide.

In an embodiment, the sleeve maintains a fixed position when the nut isrotated. In an embodiment, an outer surface of the sleeve is configuredto attach a revolute joint.

In an aspect, the disclosure provides a one degree of freedom (DoF) ofmovement device that includes: a first support member having a first endand a second end, wherein a distal portion of the first end is threadedand the second end includes a fixed mounting portion; a second supportmember having a first end and a second end wherein a distal portion ofthe first end is smooth and the second end includes a fixed mountingportion; a threaded coupling configured to mate with the threaded firstend of the first support member; a slidable coupling configured toslidably engage with the smooth first end of the second support member;a first crossbar; a second crossbar; and at least five revolute joints,wherein a first revolute joint couples a first end of the first crossbarto the threaded coupling, a second revolute joint couples a second endof the first crossbar to the fixed mounting portion of the secondsupport member, a third revolute joint couples a first end of the secondcrossbar to the slidable coupling, a fourth revolute joint couples asecond end of the second crossbar to the fixed mounting portion of thefirst support member, and a fifth revolute joint couples the firstcrossbar to the second crossbar, wherein the at least five revolutejoints confer one DoF of movement to the device.

In an aspect, the disclosure provides a vertebral body manipulationinstrument (VBMI), including: a first support member having a first endand a second end, wherein a distal portion of the first end is threadedand the second end includes a fixed mounting portion and is configuredto attach to a first vertebral anchor; a second support member having afirst end and a second end wherein a distal portion of the first end issmooth and the second end includes a fixed mounting portion and isconfigured to attach to a second vertebral anchor; a threaded couplingconfigured to mate with the threaded first end of the first supportmember; a slidable coupling configured to slidably engage with thesmooth first end of the second support member; a first crossbar; asecond crossbar; and at least five revolute joints, wherein one revolutejoint connects a middle portion of the first crossbar to a middleportion of the second crossbar to form a X-shaped structure in which thefirst crossbar spans between the threaded coupling and the fixedmounting portion of the second support member and the second crossbarspans between the slidable coupling and the fixed mounting portion ofthe first support member, and the VBMI is configured to maintain a headof the first vertebral anchor at the same relative orientation and levelof a head of the second vertebral anchor. In an embodiment, theinstrument is configured to adjust the distance between the head of thefirst vertebral anchor and the head of the second vertebral anchor. Inan embodiment, the instrument is configured to manipulate one or morevertebral bodies by applying a rocking and/or twisting motion to thefirst and/or second vertebral anchors which have been anchored in theone or more vertebral bodies.

In an aspect, the disclosure provides a method of manipulating at leastone vertebral body, including the steps of placing a first vertebralanchor in a first vertebral body; placing a second vertebral anchor in asecond vertebral body; attaching a vertebral manipulation device to ahead portion of the first vertebral anchor and a head portion of thesecond vertebral anchor; and maintaining, while manipulating at leastone vertebral body, the head portion of the first vertebral anchor atthe same relative orientation and level as the head portion of thesecond vertebral anchor. In an embodiment, manipulating the at least onevertebral body occurs by applying a rocking and/or twisting motion tothe first and/or second vertebral anchors.

Other aspects and embodiments of the disclosure are discussed below.

Definitions

The instant disclosure is most clearly understood with reference to thefollowing definitions:

As used in the specification and claims, the singular form “a,” “an,”and “the” include plural references unless the context clearly dictatesotherwise.

As used herein, the term “comprising” or “including” is intended to meanthat the compositions, methods, devices, apparatuses and systems includethe recited elements, but do not exclude other elements. “Consistingessentially of,” when used to define compositions, devices, apparatuses,systems, and methods, shall mean excluding other elements of anyessential significance to the combination. Embodiments defined by eachof these transition terms are within the scope of this disclosure.

Ranges provided herein are understood to be shorthand for all of thevalues within the range. For example, a range of 1 to 50 is understoodto include any number, combination of numbers, or sub-range from thegroup consisting 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34,35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50 aswell as all intervening decimal values between the aforementionedintegers such as, for example, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8,and 1.9. With respect to sub-ranges, “nested sub-ranges” that extendfrom either end point of the range are specifically contemplated. Forexample, a nested sub-range of an exemplary range of 1 to 50 maycomprise 1 to 10, 1 to 20, 1 to 30, and 1 to 40 in one direction, or 50to 40, 50 to 30, 50 to 20, and 50 to 10 in the other direction.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and desired objects of thepresent disclosure, reference is made to the following detaileddescription taken in conjunction with the accompanying drawing figureswherein like reference character denote corresponding parts throughoutthe several views and wherein:

FIG. 1A is a perspective view of a vertebral body manipulation deviceaccording to an exemplary embodiment of the present disclosure.

FIG. 1B is a perspective view of a vertebral body manipulation deviceattached to vertebral bodies according to an exemplary embodiment andfurther illustrating the orthogonal translations capable by such aninstrument. The Left-Posterior-Superior (LPS) patient coordinate systemis also shown, together with the arrows describing the maneuverabilitythat the device provides in the LPS directions.

FIG. 2 is an illustrative view of two devices used to manipulate a pairof vertebral bodies, one on each side (left and right) of the spinedevice according to an exemplary embodiment of the present disclosure.

FIG. 3 is a kinematic diagram of the vertebral body manipulation deviceaccording to an exemplary embodiment of the present disclosure and its 3DoF operation. Anterior-Posterior (AP), Superior-Inferior (SI), andLeft-Right (LR) directions of the Left-Posterior-Superior (LPS) patientcoordinate system are labeled.

FIG. 4 is an illustrative view of the five DoF of relativemaneuverability between the vertebral bodies provided by the vertebralbody manipulation device according to an exemplary embodiment of thepresent disclosure. Translations/rotations relative to the AP, SI, andLR directions of the LPS patient coordinate system are shown.

FIG. 5 is an illustrative view of the sixth DoF of relativemaneuverability between the vertebral bodies provided by the vertebralbody manipulation device according to an exemplary embodiment of thepresent disclosure. Rotations relative to the LR directions of the LPSpatient coordinate system are shown.

FIG. 6A is a perspective view of a module of the vertebral bodymanipulation device according to an exemplary embodiment of the presentdisclosure.

FIG. 6B is a cross-sectional view of a nut assembly coupled to athreaded pole of the vertebral body manipulation device according to anexemplary embodiment of the present disclosure.

FIG. 6C is a cross-sectional view of a module of the vertebral bodymanipulation device according to an exemplary embodiment of the presentdisclosure.

FIG. 6D is a cross-sectional view of a quick-lock mechanism of thevertebral body manipulation device in a closed (left panel) and opened(right panel) position according to an exemplary embodiment of thepresent disclosure.

FIG. 6E is a cross-sectional view of a nut assembly coupled to athreaded pole of the vertebral body manipulation device according to anexemplary embodiment of the present disclosure.

FIG. 7 is an illustrative view of the vertebral body manipulation deviceaccording to an exemplary embodiment of the present disclosure withpedicle screw locking plungers.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure features a vertebral body manipulation devicethat is simpler, smaller, and provides more degrees of freedom (DoF) ofmovement than currently available instrumentation. The vertebral bodymanipulation device of the present disclosure is based, at least inpart, on the discovery that incorporating both a threaded connectionjoint and a smooth connection joint into a scissor mechanism having an Xconfiguration may provide a module having one DoF of maneuverability inand of itself. Moreover, the vertebral body manipulation device of thepresent disclosure may provide five or six DoF of maneuverabilityrelative to the heads of the vertebral anchors to which it is attachedwhen used in pairs of two or more devices. Advantageously, the presentdevice provides two pin connection joints within the scissor mechanismhaving an X configuration that may be connected directly to quick-lockmechanisms configured to mate with a screw extension and/or vertebralanchor, which provides a more compact design that also has the benefitof keeping the heads of the vertebral anchors (e.g., pedicle screws)aligned and thereby facilitates placement of a rod. The heads of thescrews are oriented towards one another and at the same level whichguarantees the placement of a straight rod over the heads, without theneed to profile or adjust it. Additionally, the threaded connectionjoint reduces internal friction of the mechanism, thereby enhancing theforce-feedback of the device and providing the surgeon with a betterrepresentation of the forces exerted by the device on the vertebralbodies.

Abnormal curvature of the spine is referred to as spinal deformity, oneof the oldest and most common diseases [Heary R F, Madhavan K:Neurosurgery. September 2008; Vol. 63(3 Suppl) pp. 5-15]. The causes ofspinal deformity are numerous and may include congenital, degenerative,neoplastic, infectious, traumatic, iatrogenic and idiopathic etiologies[Watters W C, et al., Spine J. July 2009; Vol. 9(7) pp. 609-614].Spondylolisthesis is a form of spinal deformity commonly associated withdegenerative spondylosis. The deformity usually occurs in the lumbar andsacral regions of the spine and may affect sagittal balance [Barrey C,et al., European Spine Journal. September 2007; Vol. 16(9) pp.1459-1467, El-Rich MAC, et al. Stud Health Technol Inform. 2006; Vol.123 pp. 341-344, Labelle H, et al., Spine (Phila Pa 1976). Mar. 15,2005; Vol. 30(6 Suppl) pp. S27-34, and Barrey C, et al., Eur Spine J.September 2007; Vol. 16(9) pp. 1459-1467]. Spondylolisthesis is theanterior subluxation of one vertebral body on another, usually L5 on S1,or L4 on L5. Spinal deformity, including scoliosis, occurs frequentlyand may be as high as 68% in elderly populations [Ailon T, et al.,Neurosurgery. October 2015; Vol. 77 Suppl 4 pp. S75-91].Spondylolisthesis occurs in about 5.8% of men and 9.1% of women, withmany cases being asymptomatic [Ettinger B, et al., J Bone Miner Res.April 1992; Vol. 7(4) pp. 449-456 and Schwab F, et al., Spine (Phila Pa1976). May 1, 2005; Vol. 30(9) pp. 1082-1085]. Spondylolisthesis cancause neurological deficit from neural compression.

Surgical treatment for spondylolisthesis usually involves laminectomy todecompress the neural elements, maneuvers to re-align sagittal and/orcoronal balance, and arthrodesis to hold the new alignment [Hresko M T,et al., Spine (Phila Pa 1976). Sep. 15, 2007; Vol. 32(20) pp. 2208-2213and Kepler C K, et al., Orthop Surg. February 2012; Vol. 4(1) pp.15-20]. To accomplish the realignment, a reduction with pedicle screwsfollowed by interbody fusion with posterolateral fusion is commonlyperformed. The fixation is commonly done with implanted pedicle screwsand titanium rods attached to the screws. The reduction is achieved withsuperior-inferior (SI) and anterior-posterior (AP) actions to createdistraction-compression and subluxation-slippage translation of thevertebral bodies, respectively. Multiple studies have compared treatmentapproaches [Slone R M, et al., Radiographics. May 1993; Vol. 13(3) pp.521-543, and Weinstein eta 1., N Engl J Med. May 31, 2007; Vol. 356(22)pp. 2257-2270], and clinical guidelines for spondylolisthesis have beendeveloped by the North American Spine Society (NASS) [Watters W C, etal., Spine J. July 2009; Vol. 9(7) pp. 609-614], offering guidance toclinicians when encountering this pathology.

The instrumentation currently available for reduction takes the shape ofpliers. This often requires multiple instruments (for example fordistraction or compression) and steps to achieve the correction, makingthe procedure technically challenging and difficult to maintain,especially while changing from one instrument or maneuver to another.The pliers also require the rods to be placed between the pedicle screwheads before the correction. Unfortunately, this limits the ability tomaneuver the vertebral bodies.

Moreover, these devices have been developed for the classic opensurgery. The ability to correct deformities and perform the operationswith minimally invasive percutaneous techniques [Chrastil J, Patel A A:J Am Acad Orthop Surg. May 2012; Vol. 20(5) pp. 283-291, Kasliwal M K,et al., J Neurosurg Spine. August 2012; Vol. 17(2) pp. 128-133, OgilvieJ W: Spine (Phila Pa 1976). Mar. 15, 2005; Vol. 30(6 Suppl) pp. S97-101,Quraishi N A, et al., European Spine Journal. Dec. 19, 2012, Sansur C A,et al. J Neurosurg Spine. November 2010; Vol. 13(5) pp. 589-593, Smith JS, et al., Spine (Phila Pa 1976). Nov. 1, 2012; Vol. 37(23) pp.1975-1982, Smith J S, et al., Spine (Phila Pa 1976). May 20, 2011; Vol.36(12) pp. 958-964. Chen L, et al, Chin Med J (Engl). January 2003; Vol.116(1) pp. 99-103, Kasliwal M K, et al. Neurosurgery. July 2012; Vol.71(1) pp. 109-116, Tian N F, Xu H Z: lint Orthop. August 2009; Vol.33(4) pp. 895-903, Fu T S, et al., Int Orthop. August 2008; Vol. 32(4)pp. 517-521, Schlenk R P, et al., Neurosurg Focus. January 15 2003; Vol.14(1) pp. e2] has improved and was made possible by intraoperativefluoroscopic and computed tomography (CT) image guidance [Tian N F, Xu HZ: IInt Orthop. August 2009; Vol. 33(4) pp. 895-903 and Fu T S, et al.,Int Orthop. August 2008; Vol. 32(4) pp. 517-521]. However, instrumentsto correct the deformity using minimally invasive procedures are limitedand plier-type instruments are normally unsuitable for these procedures.

In general, forces required to correct spinal deformity are largelyunknown [Schlenk R P, et al., Neurosurg Focus. Jan. 15, 2003; Vol. 14(1)pp. e2]. It is therefore likely that these are highly variable betweendifferent surgical techniques and among surgeons. Correction forces areexerted on the screws and respectively on the vertebral bodies duringthe operation, and excessive loads may lead to bone fracture. Moreover,these forces may be falsely perceived by the surgeon, due to limitationsof the instruments used. Current deformity correction devices lack thiscapability. The vertebral body manipulation device described hereinpresents several advantages over currently available instrumentation.

Referring now to the various figures of the drawing wherein likereference characters refer to like parts, there are shown in FIG. 1A andFIG. 1B illustrative views of a vertebral body manipulation device 100of the present disclosure.

FIG. 1A shows an exemplary vertebral body manipulation device 100according to the disclosure, which includes a module 110 having two baseunits 120, which may be interconnected by a scissor mechanism 174 havingan X configuration (e.g., a scissor X mechanism). Base unit 120 mayinclude a quick-lock mechanism 150 configured to allow base unit 120 toattach to a screw extension 104, which may in turn be configured toattach to a pedicle screw 102. Quick-lock mechanism 150 also includesbutton 112 which engages the quick-lock mechanism 150, described indetail below.

Scissor X mechanism 174 may include four revolute joints 122 and acentral joint 124. Two of the four revolute joints 122 may be mounted toa base unit 120, one of the revolute joints 122 may be mounted tothreaded coupling 133, and one of the revolute joints 122 may be mountedto slidable coupling 121. Threaded coupling 133 may be configured tomate with threaded pole 106, while slidable coupling 121 may beconfigured to mate with and slidably engage smooth pole 108. Threadedpole 106 includes a nut assembly 140, described further below, whichincludes a nut 132 and a threaded surface 144. In general terms, thecombination of threaded pole 106 with a base unit 120 may be consideredas a first support member, while the combination of smooth pole 108 witha base member 120 may be considered as a second support member.

FIG. 1B depicts vertebral body manipulation device 100 attached tovertebral bodies 116. Wrench 114 may be placed on the threaded pole 106of the vertebral body manipulation device 100 and configured tomanipulate threaded coupling 133 of scissor X mechanism 174 up or downthreaded pole 106 (hidden from view under wrench 114) to operate thedevice. In some embodiments, wrench 114 may be a torque wrench.Anterior-Posterior (AP), Superior-Inferior (SI), and Left-Right (LR)axes are labeled. Smooth pole 108 may be configured to engage to scissorX mechanism 174 via any of a variety of slidable couplingconfigurations. Threaded pole 106 may be configured to engage with baseunit 120, which also includes button 112.

In embodiments, vertebral body manipulation device 100 provides a methodof manipulating at least one vertebral body, that includes the steps ofplacing a first vertebral anchor in a first vertebral body; placing asecond vertebral anchor in a second vertebral body; attaching avertebral manipulation device to a head portion of the first vertebralanchor and a head portion of the second vertebral anchor; andmaintaining, while manipulating at least one vertebral body, the headportion of the first vertebral anchor at the same relative orientationand level as the head portion of the second vertebral anchor.

In embodiments, screw extension 104 and pedicle screw 102 may be any ofa variety of commercially available screw extensions and pedicle screws.Alternatively, a screw extension 104 could be specifically designed tomanipulate pedicle screw 102 in conjunction with the vertebral bodymanipulation device 100.

As the vertebral body manipulation device and functionalities thereofare intended for use with a body, the materials shall be any of a numberof bio-compatible materials presently known or hereinafter developed.Such materials also shall be suitable for the forces and loads that canoccur during usage of the instrument. In addition, while particularshapes or geometries are described herein, it is within the scope of thepresent disclosure for other shapes or geometries to be used as long asthe described translational and rotational functional aspects can becarried out using such shapes or geometries.

The modules 110 for such a vertebral body manipulation device 100 areconfigured and arranged as needed for correcting the deformity. Asdescribed in further detail herein, each module has three DoF withuncoupled orthogonal translations, and may provide five or six DoF whenused in combinations of two or more modules 110.

Vertebral body manipulation device is unique in that it may be used incombination with almost any of a number of currently available vertebralanchors (e.g., spinal pedicle screw instrumentation). It also is usablewith both “open” surgical procedures and percutaneous pedicle screwtechniques. It allows for continuous adjustment and allows formanipulation of the vertebral segment to occur with an intuitiveuncoupled motion.

As depicted in FIG. 2, a plurality of vertebral body manipulationdevices 100 may be used. In particular embodiments, two vertebral bodymanipulation devices 100 are typically used to manipulate vertebralbodies 116, one on each side (left and right) of the spine. When used incombinations of two or more modules 110, the vertebral body manipulationdevice 100 of the present disclosure may provide five or six DoF ofmaneuverability when used.

FIG. 3 depicts a kinematic diagram illustrating the orthogonaltranslations capable according to the vertebral body manipulation deviceinstrument of the present disclosure. As described herein, operation ofthe vertebral body manipulation device 100 provides 3 degrees of freedom(DoF) of relative maneuverability between the heads of the screws 102 towhich it is attached, as shown in FIG. 2. The DoF are in theAnterior-Posterior (AP), Superior-Inferior (SI), and Left-Right (LR)directions of the Left-Posterior-Superior (LPS) patient coordinatesystem, represented in FIG. 1B and FIG. 3. The DoF provided by onedevice are:

-   -   SI maneuverability for either distraction or compression is        achieved by spinning the nut (si).    -   AP maneuverability in either direction is performed by rocking        the entire device in a quasi-sagittal plane as shown by the (ap)        arrow.    -   LR maneuverability in either direction is performed by rotating        the device in a quasi-coronal plane as shown by the (1 r) arrow.

A novel aspect of the kinematics of vertebral body manipulation device100 described herein, relative to prior art instruments (e.g., X-Press),is that the vertebral body manipulation device 100 maintains the headsthe pedicle screws 102 parallel and at the same level. Unlike all otherprior art devices, this ensures that a straight bar may be connectedbetween the heads and eliminates the need to bend the bar prior tolocking it in the pedicle screws 102 (not shown in FIG. 3), which isoften the case with prior art tools.

The DoF of relative maneuverability between the vertebral bodies enabledby vertebral body manipulation devices 100 are presented in FIGS. 4 and5. As shown in FIG. 4, two vertebral body manipulation devices 100provide 5 DoF of maneuverability. For example, vertebral bodymanipulation devices 100 may provide +S translation and −S (I)translation, +P rotation and −P (A) rotation, +P translation and −P (A)translation, +S rotation and −S (I) rotation, and +L translation and −L(R) translation with respect to the LPS axes shown in the lower rightsection of FIG. 4. The mobility of the vertebral bodies 116 about theseaxes depends on multiple factors that include their current positioningand the properties of interconnecting tissues and disks. The controls ofthe devices are determined with fine adjustments in surgery, typicallyperformed under X-Ray fluoroscopy guidance.

The positioning of the vertebral bodies in response the controls of thevertebral body manipulation devices 100 is also influenced by the stateof the pedicle screws 102. On most pedicle screws 102 the head of thescrew is mounted with a spherical joint 178. This spherical joint 178may be locked or unlocked (poly-axial). Pedicle screw 102 head lockingcould be used to facilitate the maneuvers, for example the ±STranslations in FIG. 4.

In the DoF analysis of FIG. 4, the only missing DoF is the rotationabout the L axis. This could be provided if the pedicle screw 102 areunlocked, the vertebral body manipulation devices 100 are maintained inposition, and additional maneuvers are exerted with traditionalinstruments, for example on the spinous process, as shown in FIG. 5.

FIG. 5 depicts the 6^(th) relative DoF of maneuverability between thevertebral bodies 116 may be achieved by holding the location of theunlocked pedicle screws 102 heads with the vertebral body manipulationdevice 100 and maneuvering the vertebral bodies 116, for example betweenthe spinous process.

Vertebral Body Manipulation Device

A perspective view of the vertebral body manipulation device 100 isshown in FIG. 6A, and cross-sectional axes A-A and B-B, which are shownin FIGS. 6C and 6E, respectively, are noted.

As shown in FIG. 6A, scissor X mechanism 174 of module 110 may includetwo pairs of bars 118 that are interconnected with one another viacentral joint 124, thereby forming two X's, one on either side of themodule 110 relative to axis A-A. The two X's are connected to module 110via four revolute joints 122. Two of the four revolute joints 122 may bemounted to a base unit 120, one of the revolute joints 122 may bemounted to threaded coupling 133, and one of the revolute joints 122 maybe mounted to slidable coupling 121. Threaded coupling 133 may beconfigured to mate with threaded pole 106, while slidable coupling 121may be configured to mate with smooth pole 108 via bushing 128. Threadedpole 106 includes a nut assembly 140, described in FIG. 6B below, whichincludes a nut cage 134 configured to interface with nut 132.

In further embodiments, the threaded pole 106 and smooth pole 108 arehollow (e.g., pipe shaped) such that long instruments can be passed fromthe top to the bottom of the poles to access the heads of the pediclescrews 102 (not shown in FIG. 6A). Moreover, the bars 118 of therevolute joints 122 of the scissor mechanism 174 are mounted onto eitherfixed couplings (e.g., the lower revolute joints 122 mounted to baseunits 120) or the threaded coupling 133 or the slidable coupling 121 onthreaded pole 106 and/or smooth pole 108. In the design describedherein, any length of bar 118 is contemplated, and one of skill in theart will appreciate that this will vary depending upon the particularapplication. In general, the connection heights of revolute jointsaccording to the invention will be minimized so that the joints arecentered on the threaded pole 106 and smooth pole 108. Alternatively,these 4 revolute joints 122 may also be designed on opposite sides ofthe threaded pole 106 and smooth pole 108 (e.g., relative to axis A-A),if the threaded pole 106 and smooth pole 108 need to be brought intocloser proximity. Placing the scissor X mechanism 174 on both sides isredundant, but may create a structure with improved stiffness.

Base units 120 may include button 112, which is configured to active adouble cam closure mechanism that includes latch 126, and is furtherdetailed below in FIG. 6C.

As shown in FIG. 6B, threaded pole 106 is threaded along its length andabout the outside surface. In further embodiments, such a threaded pole106 is a tubular shaped member. The threaded pole 106 comprises grooves142 and a thread surface 144. The threaded coupling 133 may be threadedonto the threaded rod pole 106. In yet further embodiments, the threadsurface 144 lends a mechanical advantage that allows the relativemovement of the vertebral bodies 116 (see e.g., FIGS. 4 and 5).

As depicted in FIG. 6B, threaded coupling 133 includes nut assembly 140,which further includes a nut 132, a nut cage 134 configured to interfacewith grooves 142 of threaded pole 106, bearing balls 136 positionedbetween threaded coupling 133 and nut cage 134, thread surface 144 on aninterior surface of nut cage 134, bushing surface 138, and a center ofthe nut 146. A rotary joint 182 is implemented between the nut 132 andthe nut-cage 134 with two rows of bearing balls 136. While two bearingballs 136 are depicted, one of skill in the art will appreciated thenumber of bearing balls 136 within rotary joint 182 may be varied asdesired.

Screw head locking can be achieved, for example, by locking nut 132 ofthe screw, or by using the quick-lock mechanism 150 (not shown) of thevertebral body manipulation device 100.

Due to the vertebral body manipulation device 100 kinematics as shown inFIG. 3, load in the SI direction generates lateral load between thepedicle screw 102 and the nut 132. Typical screw connections are notwell suited for lateral loads, because of the wedging effect of thescrew flanks. Instead, a modified ACME type thread with the bushing-nut(B-Nut) design shown in FIG. 6B was used. The ends of the nut 132present cylindrical surfaces that are in a bushing surface 138 with theouter surface (major diameter) of the threaded pole 120. The actualthread of the nut 132 is only located at the center of the nut 146 wherea larger clearance exists. To do so, the thread of the nut 132 has to berecessed deeper than the bushings surfaces 138, and therefore threadstart grooves 142 are needed at the ends of the nut thread. The bushingsurfaces 138 at the ends of the nut maintain clearance on the flanks ofthe thread surfaces 144.

As such, the screw is sized as an ACME thread screw of major diameter D.The bushings surfaces 138 (not shown) of the nut 132 are sized to with aH7/h6 tolerance from D. The thread 144 on the nut 132 is sized so thatclearance between the flank surfaces of thread exists even if thebushing 128 is loaded laterally. That is:

C _(Min) ^(T) =C _(Max) ^(B) sin α  (Equation 1)

where C_(Min) ^(T) is the minimum clearance on the thread flank, C_(Max)^(B) is the maximum clearance of the bushing 128, and α is the angle ofthe thread flank (29° for the ACME thread). The design enables thelateral loads on the thread by eliminating the high friction wedgingeffect with a built-in bushing on the screw outer diameter. The gain isin lieu of a minimum axial backlash of the nut 132 relative to thescrew.

B _(Min) =C _(Max) ^(B) sin 2α  (Equation 2)

The backlash is typically larger than that of a regular screw, whereflank clearance may be used to control the backlash.

According to another aspect of the present disclosure there is featuredan implant system embodying such a vertebral body manipulation device100 described herein and a spinal implant as is known to those skilledin the art. In further embodiments, the spinal implant is operablycoupled to the vertebral body manipulation device.

FIG. 6C shows a cross-sectional view of a module 110 of the vertebralbody manipulation device according to an exemplary embodiment of thepresent disclosure along the A-A axis as noted in FIG. 6A. Threaded pole106 may be configured to couple with threaded coupling 133 via nut 132and nut cage 134, which interface on one surface directly with grooves142 of threaded pole 106 while the opposite surface interfaces with theinterior surface of threaded coupling 133 via rotary joint 186.

The smooth pole 108 may be configured to couple with slidable coupling121 via bushing 128. Bars 118 and central joint 124 are shown forreference.

Quick-lock mechanism 150 may be configured to seat on or mate with screwextensions 104 to attach vertebral body manipulation device 100 with oneor more vertebral anchors (not shown). Each screw extension 104 isfitted within receiving hole 154 of either threaded pole 106 or smoothpole 108. A latch 126 secures the screw extension 104 in position withinthe receiving hole 154 by inserting into geometric feature 125 when inthe actuated position, thereby locking screw extension 104 into place.The latch 126 is actuated by a double-cam mechanism, including surfacesof the latch 126, the button 112, spring 148, and button-end part 152.

FIG. 6D is a cross-sectional view of a quick-lock mechanism of thevertebral body manipulation device in a closed (left panel) and opened(right panel) position according to an exemplary embodiment of thepresent disclosure. As depicted in FIG. 6D, when the button 112 ispressed (right panel), the top cam (button 112 to latch 126) pulls thelatch 126 away from the geometric feature 125, which allows screwextension 104 to be inserted into and/or removed from receiving hole154. When button 112 is pressed, the cam is in the unactuated (e.g.,open) configuration.

When the button 112 is released (left panel of FIG. 6D), the spring 148pushes up the button-end part 152, so that the bottom cam (button-end tolatch, 152 to 126) pushes the latch 126 back into geometric feature 125,which locks screw extension 104 into place. After pushing the latch 126,the button-end part 152 also locks the latch 126 in the closed positon,as shown in the FIG. 6D, this ensuring a positive lock of the extension.When button 112 is released, the cam is in the actuated (e.g., closed)configuration.

FIG. 6E is a cross-sectional view along axis B-B of FIG. 6A of a nutassembly coupled to a threaded pole 106 of the vertebral bodymanipulation device 100 according to an exemplary embodiment of thepresent disclosure. Also visible in FIG. 6E is the design of the bearingballs 136. For each bearing ball 136, a channel 162 is made within thenut-cage 134 to allow the bearing balls 136 to be fed within theirraces, between the nut 132 and the nut-cage 134, that form the races ofthe bearing. While two bearing balls 136 are visible in FIG. 6E, one ofskill in the art will appreciate that any number of bearing balls 136appropriate for the size and configuration of the race may be used. Thechannels 162 are then closed with plugs 158. In embodiments, designconsideration may be given to reduce the internal friction of themechanism under load by, for example, adding additional bearings.Revolute joints 122 may be built with joint bearings 138 to reducefriction. A joint may be made, for example, by two rows of bearing balls138 that sandwich one of the bars 118 with a bearing-race screw 156.

In further embodiments, the design of the vertebral body manipulationdevice 100 is optimized to reduce the change of its mechanical advantagedue to the change in the relative angulation of the scissor X mechanism174. FIG. 3 shows the location of the 4 side revolute joints 122 on theside of the threaded pole 106 and smooth pole 108, for the clarity ofthe schematic. However, in the design the length of the respective linksis zero or negative (on the opposite side of the threaded pole 106 andsmooth pole 108). The location of the revolute joints 122 relative tothe threaded pole 106 and smooth pole 108 may be optimized to reducesharp angles of the scissor X mechanism bars 174.

Pedicle Screw Lock

Pedicle screws 102 include ways to secure them to the connecting rodsand lock their ball joint (from poly-axial to mono-axial in spinesurgery terms). As shown in the cross section views of FIGS. 6C and 6E,both threaded pole 106 and smooth pole 108 of the vertebral bodymanipulation device 100 are hollow. Their inner diameter is large enoughto allow the passage of the nut 132 of the pedicle screw 102 and itslong wrench 114. If a rod is set in place over the screw head, the nut132 can lock the head of the screw 102. This is typically performedafter achieving the correction of deformity, so that the correction issecured by the screw-rod implant system.

As the vertebral body manipulation device 100 of the present disclosureembodies a quick lock mechanism 150 for coupling the instrument to anyof a number of currently vertebral anchors, such as those embodying autilizing polyaxial screw, such a vertebral body manipulation device iseasily adaptable to use such a vertebral anchor.

According to further aspects, the present disclosure also featuremethods for stabilizing a spine using such an implant system and/orreduction instrument/device as described herein. Also featured aremethods for treating spondylolithesis using surgical techniques andusing the vertebral body manipulation device and/or implant system ofthe present disclosure. Such methods are usable with both “open”surgical procedures and percutaneous pedicle screw techniques. Suchmethods further include continuous adjustment and manipulation of thevertebral segment to occur with intuitive uncoupled motion.

Such methods include providing one or more modules comprising any of theabove described vertebral body manipulation device 100 and localizingthe one or more modules 110 to a spinal implant and securing thevertebral body manipulation device to the spinal implant. The vertebralbody manipulation device 100 includes an alternative screw-head lockingmechanism that enables locking prior to placing the rods. Two lockplunger assemblies 170 are shown in FIG. 7, one placed in the primarydevice 130, the other separately.

In embodiments, the plunger assembly 170 consists of a threaded cap 166that spins over a plunger 168. A plunger assembly 170 is placed througha threaded pole 106 or smooth pole 108 (e.g., via a smooth pole hole164) and threaded cap 166 threads into the head of the screw extension104. Tightening the thread pushes the plunger 168 down through thethreaded pole 106 or smooth pole 108 and screw extension 104, so thatthe end surface of the plunger 172 locks the pedicle screw 102 byforcing it against its head.

In further embodiments, such methods further include performing othersurgical techniques related to the surgical treatment of the underlyingcondition. Such other surgical techniques include fusion of adjacentvertebrae, bone grafting, discotomy, decompression or laminectomy andspinal implants. Additionally such methods for treating furtherincludes, wound care and minimizing onset of infection.

Although a preferred embodiment of the disclosure has been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

INCORPORATION BY REFERENCE

All patents, published patent applications, and other referencesdisclosed herein are hereby expressly incorporated by reference in theirentireties.

EQUIVALENTS

Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents of the specificembodiments of the disclosure described herein. Such equivalents areintended to be encompassed by the following claims.

1. A vertebral manipulation instrument, comprising: at least one moduleincluding a first base unit, a second base unit, a threaded pole, asmooth pole, and a scissors mechanism; the first base unit having anupper end connected to the threaded pole and a lower end configured tomate with a first vertebral anchor; the second base unit having an upperend connected to the smooth pole and a lower end configured to mate witha second vertebral anchor; and the scissors mechanism connecting thefirst base unit to the second base unit and the threaded pole to thesmooth pole.
 2. The vertebral manipulation instrument of claim 1,wherein the scissors mechanism connects to the first base unit and thesecond base unit via a revolute joint.
 3. The vertebral manipulationinstrument of claim 1, wherein the scissors mechanism connects to thethreaded pole via a revolute joint mounted on a threadable couplingconfigured to interface with a threaded portion of the threaded pole. 4.The vertebral manipulation instrument of claim 1, wherein the scissorsmechanism connects to the smooth pole via a revolute joint mounted on aslidable coupling configured to interface with a smooth portion of thesmooth pole.
 5. The vertebral manipulation instrument of claim 1,wherein the vertebral manipulation instrument is able to convey threedegrees of freedom of movement to the first and second vertebral anchorswhen the lower end of the first base unit is mated with the firstvertebral anchor and the lower end of the second base unit is mated withthe second vertebral anchor.
 6. The vertebral manipulation instrument ofclaim 1, wherein the first base unit and the second base unit each havea quick-lock mechanism configured to secure the first and secondvertebral anchors.
 7. The vertebral manipulation instrument of claim 3,wherein the threadable coupling includes a rotary joint.
 8. Thevertebral manipulation instrument of claim 3, wherein the threadablecoupling includes a nut and a nut cage configured to interface with aplurality of grooves on the threaded pole and a plurality of bearingballs positioned between the threaded coupling and the nut cage, the nutincluding a recessed thread configured to provide clearance relative tothe plurality of grooves on the threaded pole.
 9. A method for surgicaltreatment of spondylolithesis comprising the step(s) of: providing thevertebral manipulation instrument of claim 1, wherein each of the atleast one modules is configured and arranged to cause translation orrotation of a vertebral segment along an Anterior-Posterior (AP),Superior-Inferior (SI), and/or Left-Right (LR) axis of aLeft-Posterior-Superior (LPS) patient coordinate system.
 10. Thesurgical treatment method of claim 9, further comprising the step(s) of:securing the manipulation instrument to a spine using spinal pediclescrew instrumentation.
 11. The surgical manipulation instrument of claim1, wherein the scissors mechanism confers three degrees of freedom ofmovement to the first and second vertebral anchors when the lower end ofthe first base unit is mated with the first vertebral anchor and thelower end of the second base unit is mated with the second vertebralanchor.
 12. The surgical manipulation instrument of claim 11, whereinthe scissors mechanism connects to the threaded pole via a revolutejoint mounted on a threadable coupling configured to interface with athreaded portion of the threaded pole.
 13. The surgical manipulationinstrument of claim 12, wherein the threadable coupling is operated witha wrench.
 14. The surgical manipulation instrument of claim 13, whereinthe wrench is a torque wrench.
 15. The surgical manipulation instrumentof claim 11, wherein the scissor mechanism is configured to reducechanges in mechanical advantage.
 16. The surgical manipulationinstrument of claim 11, wherein the instrument is configured to maintaina head of the first vertebral anchor at the same relative orientationand level of a head of the second vertebral anchor.
 17. The surgicalmanipulation instrument of claim 16, wherein instrument is configured toadjust the distance between the head of the first vertebral anchor andthe head of the second vertebral anchor.
 18. The surgical manipulationinstrument of claim 11, wherein the instrument is configured tomanipulate one or more vertebral bodies by applying a rocking and/ortwisting motion to the first and/or second vertebral anchors which havebeen anchored in the one or more vertebral bodies. 19-23. (canceled) 24.A one degree of freedom (DoF) of movement device, comprising: a firstsupport member having a first end and a second end, wherein a distalportion of the first end is threaded and the second end includes a fixedmounting portion; a second support member having a first end and asecond end wherein a distal portion of the first end is smooth and thesecond end includes a fixed mounting portion; a threaded couplingconfigured to mate with the threaded first end of the first supportmember; a slidable coupling configured to slidably engage with thesmooth first end of the second support member; a first crossbar; asecond crossbar; and at least five revolute joints, wherein a firstrevolute joint couples a first end of the first crossbar to the threadedcoupling, a second revolute joint couples a second end of the firstcrossbar to the fixed mounting portion of the second support member, athird revolute joint couples a first end of the second crossbar to theslidable coupling, a fourth revolute joint couples a second end of thesecond crossbar to the fixed mounting portion of the first supportmember, and a fifth revolute joint couples the first crossbar to thesecond crossbar, wherein the at least five revolute joints confer oneDoF of movement to the device, or. a vertebral body manipulationinstrument (VBMI), comprising: a first support member having a first endand a second end, wherein a distal portion of the first end is threadedand the second end includes a fixed mounting portion and is configuredto attach to a first vertebral anchor; a second support member having afirst end and a second end wherein a distal portion of the first end issmooth and the second end includes a fixed mounting portion and isconfigured to attach to a second vertebral anchor; a threaded couplingconfigured to mate with the threaded first end of the first supportmember; a slidable coupling configured to slidably engage with thesmooth first end of the second support member; a first crossbar; asecond crossbar; and at least five revolute joints, wherein one revolutejoint connects a middle portion of the first crossbar to a middleportion of the second crossbar to form a X-shaped structure in which thefirst crossbar spans between the threaded coupling and the fixedmounting portion of the second support member and the second crossbarspans between the slidable coupling and the fixed mounting portion ofthe first support member, and the VBMI is configured to maintain a headof the first vertebral anchor at the same relative orientation and levelof a head of the second vertebral anchor. 25-27. (canceled)
 28. A methodof manipulating at least one vertebral body, comprising: placing a firstvertebral anchor in a first vertebral body; placing a second vertebralanchor in a second vertebral body; attaching a vertebral manipulationdevice to a head portion of the first vertebral anchor and a headportion of the second vertebral anchor; and maintaining, whilemanipulating at least one vertebral body, the head portion of the firstvertebral anchor at the same relative orientation and level as the headportion of the second vertebral anchor.
 29. (canceled)